1. Field of the Invention
The invention relates to the field of well refurbishing, and more specifically to cleaning devices for use in cleaning well casings.
2. Description of Related Art
Well casings have perforations, vertical slots in the wall of the casing that let the water flow into the casing. These perforations are small enough that rocks and other debris are prevented from entering the inside of the casing. The casing is disposed in the earth so that only the perforated area is positioned in the ground formation where the water is located.
After a period of time, the perforations in well casing can become closed due to corrosion or bacterial growth, with scale and rust forming on the inside of the casing. This corrosion causes a decrease in the volume of water that can flow into casing to be pumped out, and over time the flow of the water can be decreased drastically, and in some cases, to the point that the well can not produce enough flow to be profitable and must be abandoned. Well casing refurbishing is done to increase the volume of water that can flow into the well casing during a pumping operation. By opening up the perforations and cleaning the casing, the volume of water that can freely flow into the casing increases. Several methods are known for refurbishing well casings.
In the bucket method, a pulling rig is used that has only the capability of up and down cable motion. Cleaning chemicals are poured into the well, and a large metal bucket is then lowered into the well casing with the rig and positioned at the bottom of the area where the perforations are located. The bucket is then pulled up rapidly and then dropped a number of times. By doing this, the water in the casing is agitated, with some loosening of the corrosion in the perforations and the rust and scale on the inside of the casing.
The effectiveness of this method is based on the cleaning chemical loosening the buildup of corrosion and scale in the perforations and casing, plus the reaction caused by the movement of the water. However, since there is no brush scrubbing the buildup on the well casing, it usually takes a number of repetitions to realize only a small improvement. The perforations are not effectively cleaned.
In the brush method, a pulling rig is again used that only has the capability of up and down cable motion. This method utilizes a device comprising a pipe with short pieces of steel cable mounted perpendicularly to the body of the pipe, forming a type of heavy metal brush. Cleaning chemicals are poured into the well, and the brush is lowered into the well casing and positioned at the bottom of the perforations. The brush is then slowly pulled up, with the steel cable scrubbing the inside of the casing and opening up some of the perforations.
The brush method is not effective in cleaning the corrosion and scale buildup all the way around the inside of the casing. Since the movement is only up and down, there are large portions of the perforated area that are not cleaned properly. This method also has the disadvantage that scale removed from the casing will be brushed into the perforations and plug them up. Moreover, care must be taken with this type of brush to limit the scrubbing so the casing is not damaged.
It is therefore an object of the invention to provide an apparatus for cleaning a well casing that effectively removes scale and corrosion around the entirety of the casing, without damaging the casing.
In order to achieve this and other objects, the invention is directed to an apparatus for cleaning a well casing comprising three components:
1. A coupling having first and second ends, the first end constructed and arranged for connection to a drill stem of a drilling rig having vertical and rotational motion and means for pumping liquid therethrough to the drill stem. The coupling has a central passageway therethrough connected to the means for pumping liquid;
2. A drill collar tube comprising a central passageway therethrough connected to the central passageway of the coupling at one end of the drill collar tube, a closure at the opposite end of the drill collar tube, an outer surface, and a plurality of nozzles disposed between the central passageway and the outer surface; and
3. A plurality of brushes extending in a direction generally outwardly from the outer surface of the drill collar tube. The brushes are preferably provided by a brush pipe assembly having a plurality of brushes extending perpendicularly from the brush pipe, the brushes being generally disposed in longitudinal rows which are separated by a plurality of longitudinal slots. The brush pipe is positioned over the drill collar tube with the slots opposite the nozzles and is secured to the drill collar tube.
The apparatus of the invention thus provides a number of improvements over the prior art.
The rotation of the brushes allows for the entire area of the perforated casing to be scrubbed by the brushes, and avoids leaving any sections not cleaned. The rotation of the brushes also allows for the bristles to actually knock the scale off the casing and not merely push the scale into the perforations.
The high pressure force used to distribute the water and/or cleaning chemical combined with the rotational motion of the apparatus distributes the water and/or cleaning chemical over the entire perforated area of the casing and into all the perforations. By using high pressure, the water and/or cleaning chemical penetrates the perforated areas more effectively, and penetrates under the scale buildup. The high pressure force opens up the perforations from the inside to the outside of the well casing, and is also very good at removing the scale buildup on the inside of the casing.
With both the rotating of the apparatus and the high pressure force cleaning the perforated area, it typically takes only one pass through the perforated section to successfully clean the area.